Next Tuesday is the 150th anniversary of the publication of On the Origin of Species. To mark the occasion, author Mary Ellen Hannibal and photographer Susan Middleton scoured the 20 million animal specimens preserved on the shelves of the California Academy of Sciences. They've presented the best in their new book Evidence of Evolution.

Many people associate collecting and preserving with the 19th-century gentleman naturalist returning home from his exotic travels armed with souvenirs. Although collecting certainly was a Victorian obsession, with museum curators keen to collect a representative of every living thing, past and present, this is still the goal today.

Many old techniques are still used, such as preserving specimens in alcohol-filled jars or removing the innards so only skin is left – birds are often preserved like this – or carefully pinning and filing them away in drawers, like these colourful beetles.